Centrifuges



Aug. 26, 1969 B. SALMON 3,463,388

CENTRIFUGES Filed Dec. 27. 1967 3,463,388 Patented Aug. 26, 1969 United States PatentOflice Int. cl. B041) us. Cl. 233-1 4 Claims ABSTRACT OF THE DISCLOSURE Improvement made in centrifuges for the interassembly of the lateral shell and of the bases of the bowls or rotary elements of machines of this type. The improvement consists in joining said shell to each of said bases with interposition of a seal by means of studs which are spaced around the periphery :of said shell and traverse said base at right angles to its plane, as well as in assembling said shell and each base in interfitting relation along a contact surface which is inclined to the center-line of said bowl and along a second surface which is perpendicular to said center line.

This invention relates to an improvement made in centrifuges, especially in regard to the assembly and construction of the bases of the bowls or rotary elements of these machines.

It is known that, for reasons of convenience of machining, the bowl of a high-speed centrifuge is usually fitted with two detachable bases and that very special care has to be taken when joining said bases to a lateral cylindrical shell, taking into account of the stresses which arise from the centrifugation velocity and which are exerted throughout the bowl. Unless certain precautions are taken, such stresses are liable to result in a defective assembly and to cause damage to the machine in a very short time.

This invention is directed to an improvement in centrifuges which specifically permits of substantially improved mechanical strength of the rotary bowl, this result being accomplished by means of a particular mode of assembly of the shell and of its two associated bases.

To this end, a centrifuge in accordance with the invention comprises a bowl formed of a lateral shell and two bases, and is characterized in that said shell and each of said bases are assembled together with interposition of a seal by means of studs which are spaced around the periphery of said shell and traverse said base at right angles to its plane, said base and said shell being assembled in interfitting relation along a contact surface which is inclined to the axis of said bowl and along a second surface which is perpendicular to said axis.

Taking into account the strict symmetry of the rotary bowl about its rotational axis, the contact surface has a conical profile whose summit is located on the axis and in particular in a region located outside the bowl, the design function of said conical profile being on the one hand to ensure accurate centering of the base considered with respect to the shell and, on the other hand, to prevent any possibility of ovalization of the extremity of said shell during operatio as well as to obtain a limitation of the stresses produced at the level of the assembly between the base and the shell.

The properties and advantages outlined above will become more readily apparent from the exemplified embodiment which is described hereinafter by way of indication and not in any limiting sense.

Reference is made to the single figure of the accompanying drawings which is a diagrammatic sectional view showing a portion of a cylindrical shell and a portion of the base of a centrifuge bowl, said portions being assembled in accordance with the invention.

In this figure, there is shown a portion of a bowl 1 of a centrifuge comprising a cylindrical shell 2 which is associated at one end thereof with a detachable base 3. The interassembly of the shell and of the base is carried out by means of studs such as the stud 4 which traverse the base 3 through bores 5 located at right angles to the plane of the base considered. Each stud 4 has an extremity 6- which is intended to be screwed into an internally threaded bore of the shell 2 and is rigidly fixed in position at the other extremity thereof by means of a nut :8 which applies a washer 9 against the bottom 10 of a recess 11 formed in the base 3. The washer 9 is mounted with very small clearances both within the bore of the recess 11 and around the stud 4 in order to ensure that this: latter is centered and in particular to, prevent the displacement of said stud under the action of centrifugal force. The same function could be performed by a shoulder formed on the nut 8. A seal 12 is mounted in the face of the shell opposite to the base inside a channel 13, the design function of said seal being thus to ensure imperviousness of the bowl 1 with respect to the exterior when the nuts are screwed home.

In accordance with the invention, the assembly referredto above is carried out so that the shell 2 and its base 3 are in interfitting relation in such a manner as to ensure that these two parts come into contact along a surface 14 which is inclined to the axis (not shown) of the bowl and consequently have a conical profile, the summit of which is located on the axis externally of the bowl. To this end, the base 3 comprises a heel 15 whilst the shell 2 has a complementary taper 16 in which the heel is intended to fit.

The arrangement described above accordingly permits of accurate centering of the base with respect to the shell While leaving at 17 a small longitudinal clearance between the two parts prior to clamping and final sealing. The valve of the clearance, which can be of the order of 0.1 mm., for

example, can be estimated and controlled visually as the two parts are brought together. Reduction of said clearance to zero at the time of screwing-up produces a value of prestress such that the centering which is thus accomplished is accordingly retained regardless of the velocity of rotation of the bowl without any possibility of relative displacement of the two parts.

Interengagement of the shell 2 and of its base 3 by virtue of the conical surface 14 also makes it possible to prevent ovalization of the extremity of the shell at the level of the assembly while at the same time limiting the stresses at this point to values below the tangential stresses developed within the shell at a point which is relatively distant from the end restraint thus provided. In fact, the pressure exerted by the base 3 on the corresponding surface of the shell 2 at any point of the surface 14 makes it possible to transfer to the base which is comparable with a disc the stresses applied to the shell which is comparable with a tube. It is a known fact that the stresses in a disc are lower than those imposed on a tube of the same diameter. It is also noted that the reaction which results from the coupling force between the base and the shell by virtue of the studs 4 is essentially applied to the heel 15 and produces a moment which partially compensates for the moment which results from the centrifugal force exerted on the shell.

It is readily understood that the invention is not limited to the form of construction which has been described in the foregoing and illustrated in the accompanying drawings but extends, on the contrary, to any or all alternative forms.

What I claim is:

1. A centrifuge comprising a bowl formed of a lateral shell and two bases, characterized in that said shell and each of said bases are assembled together with interposition of a seal by means of studs which are spaced around the periphery of said shell and traverse said base at right angles to its plane, said base and said shell being assembled in interfitting relation along a contact surface which is inclined to the axis of said bowl and along a second surface which is perpendicular to said axis.

2. A centrifuge in accordance with claim 1, characterized in that said contact surface has a conical profile whose summit is located on the rotational axis in a region located outside the bowl.

3. A centrifuge in accordance with claim 1, characterized in that said base comprises a peripheral heel which is adapted to fit around a complementary tapered portion of said shell and around said second surface.

4. A centrifuge in accordance with claim 1, characterized in that said studs are located nearer the axis of said bowl than said heel and that the clamping action produced by means of said studs applies to said bowl a moment in opposition to the moment which results from centrifugal force.

References Cited UNITED STATES PATENTS 1,474,379 11/ 1923 Robertson 23329 1,595,017 8/1926 Myer et al 2331 2,263,708 11/1941 Svensjo et al. 23329 WILLIAM 1. PRICE, Primary Examiner 

